Induction stirrer



Jam@ 2% E95@ L. DREYFUS INDUCTION STIRRER Filed Nov. 19, 191:5

Patented June 27, 1950 INDUCTION STIRRER Ludwig Dreyfus, Vastera Allmanna Yasteras, Sweden,

S, Svenska Elektriska Aktiebolaget,

a corporation of Sweden Sweden, assigner to Application November 19, 1945, Serial No. 629,458 In Sweden November 30, 1944Y It is known to provide metallurgical furnaces, especially electric arc furnaces, with a multiphase electrical winding beneath the bottom of the furnace hearth, said winding being fed by low frequency alternating currents and serving to produce, by induction, a motion of the molten contents of the furnace around a, horizontal axis. Such a winding has heretofore been arranged between the masonry of the furnace and the sheet metal shell serving to support and reinforce the said masonry, the said shell consisting of magnetic iron and serving as a return path or yoke for the magnetic flux penetrating the molten furnace contents. While such a construction is quite satisfactory in electromagnetic respect, it has been found to have the disadvantage, that if the masonry should be damaged vin some way by heat or chemical action or otherwise, there is a risk of the winding being damaged by heat action.

It has now been found, that in using such low frequencies of the alternating current which are suitable for the stirring of the bath, and which in large furnaces should be about one cycle per second or less, and in manufacturing the shell V44supporting the furnace, or at least the bottom of said shell, of nonmagnetic material having a high electric resistivity, for instance of non-magnetic sheet iron, it is possible to place the stirring winding outside, i. e. beneath, the supporting shell bottom and still to induce sufficiently strong eddy currents in the bath to obtain the desired stirring action, without inducing so strong currents in the shell as to cause a non-permissible heating thereof or an appreciable loss of power therein. Because of the non-magnetic nature of the shell it forms no return path for the flux from the windings and therefore does not divert this flux from the contents of the furnace. A metallurgical furnace. especially an electric arc furnace, provided with a stirring winding arranged in this manner. forms the object of the present invention. The stirring winding should preferably be arranged in slots in a separate shell of magnetic material, said shell being preferably laminated, although with considerably thicker sheet iron than in usuallaminations. for instance with a thickness of about l centimeter or more.

A form of the invention is illustrated in the accompanying drawing in a plan view with the furnace body removed in Fig. 1 and in a side view with part of the furnace body in section ,in Fig. 2.

I represents the masonry of the furnace body, and 2 a shell serving to reinforce the said masonry at its periphery. The said shell has, at the bottom, a continuation 9 of non-magnetic sheet iron, with which .it may be connected bv a welded joint I 0. Beneath the bottom shell 9.

there is placed a, laminated shell of magnetic iron 3 with slots open upwards containing Number Name Date 1,078,619 Greene Nov. 18, 1913- l,479,582 Brayton Jan. 1, 1924 1,795,842 Davis Mar. 10, 1931 1,801,790 Breisky et al. Apr. 21, 1931 1,801,791 Breisky et a1 Apr. 21, 1931 1.823,970 Davis Sept. 22, 1931 1,851,984 Rennerfelt Apr. 5, 1932 1,862,293 Brace June 7, 1932 2,059,300 Adams Nov. 3, 1936 2,073,597 Northrup Mar. 9, 1937 2,198,304 Cornelius Apr. 23, 1940 2,256,518 Dreyfus Sept. 23, 1941 2,317,597 Ford et al Apr. 27, 1943 2,363,582 Gerber et al. Nov. 28, 1944 FOREIGN PATENTS l Number Country Date 353,523 Italy Oct. 20, 1937 499,437 Great Britain Jan. 24, 1939 523,785 Great Britain July 23, 1940 541,023 Great Britain Nov. 10, 1941 71,797 Norway Mar. 10, 1947 3 Claims. (Cl. 13 -26) a two-phase winding, which consists of acentral coil 4 fed by current lateral coils 5 fed by current of another phase, preferably with a phase diil'erence of 90.

Some of the plates forming the laminated shell may have a larger height (at 6) than is required for magnetic reasons, in order to constitute a mechanically rigid construction. 'Ihe same plates or other strengthening structures may be directly secured to the shell 2 at one end at l and connected thereto by links 8 at the other end, in order to permit a mutually different heat expansion.

I claim as my invention:

l. In a metallurgical furnace, a masonry hearth adapted to hold a liquid charge, a multiphase winding mounted below said hearth, means for feeding said winding by a, multiphase current having a frequency of the order of one cycle per second at most, and a continuous protective sheet metal shell of non-magnetic metal of high electric resistivity between said winding and said hearth, said shell reinforcing said hearth and protecting said winding against heat damage resulting from damage to said hearth.

2. In a furnace as claimed in claim 1, a shell of magnetic material below said first shell having thick laminations and provided with slots therein, said windings being mounted in said slots.

3. In a furnace as claimed in claim 2, expansion joints connecting said shells. f

LUDWIG DREYFUS.

REFERENCES CITED The following references le of this patent:

UNITED STATES PATENTS of one phase and two` are of record in the 

